Tribute to Jörn Manz

Principles of enantio-selective excitation in three-wave mixing spectroscopy of chiral molecules

“…In the gas phase, the means for enantiomer separation, conversion and purification are essentially limited to electromagnetic fields. Their use to this end has been discussed theoretically for about two decades [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. Even simply separating the two enantiomers out of a racemat is already a formidable task because of their identical spectra, except for a tiny energy difference due to the weak interaction [15,16].…”

“…A possible handle for separation arises for molecules with three non-vanishing dipole moment components, µ a , µ b , µ c , in the molecule-fixed coordinates, since one component switches sign upon change of enantiomer such that the enantiomers can exhibit a different interaction with electromagnetic radiation. Enantiomer separation exploiting this difference to achieve enantio-selective population of certain molecular states can make use of the electronic [1][2][3][4], vibrational [6,7,11], or rotational [12,13,[17][18][19][20][21][22][23] degrees of freedom of the molecule.…”

“…First theoretical proposals for enantio-selective excitation assumed the molecules to be oriented in space [1][2][3][4][5]. However, this is not a fundamental requirement since the enantiomerspecific electric-dipole interaction survives orientational averaging [8,9,24].…”